Geochemical characteristics and origin of crude oil and natural gas in different areas of Wenchang-A Sag, Pearl River Mouth Basin, South China Sea

Abstract

Complex hydrocarbon distributions characterize the Wenchang-A Sag. Systematic study of the geochemical characteristics of crude oil, natural gas and source rocks and their genetic relationship is still needs to be completed. The Rock-Eval, kerogen maceral, vitrinite reflectance, saturated hydrocarbon gas chromatography-mass spectrometry, natural gas components, carbon isotopes, and light hydrocarbon were performed. 1) Crude oil is classified based on four factors: wax content, the presence of C₂₇ diasteranes, the regular steranes αα20RC₂₇-αα20RC₂₈-αα20RC₂₉, and the bicadinanes characteristics. Class I crude oil has high wax and C₂₇ diasteranes. For Class II crude oil, the regular steranes are in ‘L’- shaped distribution, and the content of bicadinanes is shallow. Class III crude oil has soft wax and C₂₇ diasteranes, and regular steranes in the reverse ‘L’-shaped distribution, with a high peak degree of bicadinanes. For Class IV crude oil, regular steranes are in ‘V’-shaped distribution, with high peak bicadinane. 2) Class I crude oil comes from source rocks in area C. Class II crude oil comes from source rocks in areas D and E. Class III crude oil comes from areas A, and B. Class IV crude oil comes from source rocks in area A. 3) The source of natural gas in Group I is hydro propylene, and natural gas in Group II is humic. Natural gas in Group III is mixed. Groups I and II are kerogen cracking gas, and group III is a mixture of crude oil secondary cracking gas and kerogen cracking gas. Natural gas in Groups I and II mainly come from local source rocks, and Group III has mixed source characteristics. In the future, oil exploration can continue in Areas C and D, and more favorable areas for gas exploration are Areas C, D, and E.

Graphical abstract

Keywords

organic geochemistry / origin / geochemical characteristics / crude oil / natural gas

References

[1] Chen L, Fan C W, Liu X Y, Li M, Lei M Z (2021). Hydrocatbon enrichment laws and favourable exploration directions of Wenchang A sag, western Pearl River Mouth Basin.China Offshore Oil and Gas, 33(5): 14–23

[2] Chen Y, Mi T Z, Liu Y T, Li S Q, Zhen Y (2020). Microbial community composition and function in sediments from the Pearl River Mouth Basin.J Ocean Univ China, 19(4): 941–953

[3] Cheng K, Jin W, He Z, Chen J, Yang Z (1987). Composition characteristics of light hydrocarbons in continental oil and condensate and their geological significance.Petrol Explor Dev, 1: 34–43+33

[4] Cheng P, Xiao X M, Gai H F, Li T F, Zhang Y Z, Huang B J, Wilkins R W T (2015). Characteristics and origin of carbon isotopes of n-alkanes in crude oils from the western Pearl River Mouth Basin, South China Sea.Mar Pet Geol, 67: 217–229

[5] Chung H M, Gormly J R, Squires R M (1988). Origin of gaseous hydrocarbons in subsurface environments: theoretical considerations of carbon isotope distribution.Chem Geol, 71(1−3): 97–104

[6] Dai J (1990). A brief discussion on the problem of the geneses of the carbon isotopic series reversal in organogenic alkane gases.Nat Gas Ind, 10(6): 15–20

[7] Dehyadegari E (2021). Geochemistry and origins of Sarvak oils in Abadan plain: oil-oil correlation and migration studies.Energy Sources A Recovery Util Environ Effects, 43(6): 716–726

[8] Feng Z, Liu D, Huang S, Gong D, Peng W (2016). Geochemical characteristics and genesis of natural gas in the Yan’an gas field, Ordos Basin, China.Org Geochem, 102: 67–76

[9] Fu N, Li Y C, Sun X, Sun Y M, Xu J Y (2011). Recognition of oil source and source rocks in Zhu III Depression.Geoscience, 25(06): 1121–1130

[10] Gong D, Li J, Ablimit I, He W, Lu S, Liu D, Fang C (2018). Geochemical characteristics of natural gases related to Late Paleozoic coal measures in China.Mar Petrol Geol, 96: 474–500

[11] Hu G, Li J, Li J, Li Z, Luo X, Sun Q, Ma C (2008). Preliminary study on the origin identification of natural gas by the parameters of light hydrocarbon.Sci China Ser D Earth Sci, 51(S1): 131–139

[12] Huang B J, Xiao X M, Zhang M Q (2003). Geochemistry, grouping and origins of crude oils in the Western Pearl River Mouth Basin, offshore South China Sea.Org Geochem, 34(7): 993–1008

[13] HuangD F, LiJ C, ZhouN H, Gu X Z, ZhangD J (1984). The evolution of continental organic matter and the mechanism of hydrocarbon generation. Beijing: Petroleum Industry Press (in Chinese)

[14] Huang D F, Zhang D J, Li J C (1994). The origin of 4-methyl steranes and pregnanes from Tertiary strata in the Qaidam Basin, China.Org Geochem, 22(2): 343–348

[15] Huang S, Wang Z, Lv Z, Gong D, Yu C, Wu W (2014). Geochemical identification of marine and terrigenous condensates—a case study from the Sichuan Basin, SW China.Org Geochem, 74: 44–58

[16] Huang W B, Cheng J, Shao M L (2022). Discussion on organic matter abundance evaluation criteria of source rocks in deep middle-high thermal evolution stage in south Songliao Basin.Unconventional Oil & Gas, 8(2): 13–23

[17] HuntJ (1979). Petroleum Geochemistry and Geology. San Francisco: Freeman W. H.

[18] James A T (1983). Correlation of natural gas by use of carbon isotopic distribution between hydrocarbon components.AAPG Bull, 67(7): 1176–1191

[19] Jiang H, Wang H, Li J L, Chen S P, Lin Z L, Fang X X, Cai J (2009). Research on hydrocarbon pooling and distribution patterns in the Zhu-3 Depression, the Pearl River Mouth Basin.Oil Gas Geol, 30: 275–281+286

[20] JiangW M, LiY, YangC, Xiong Y Q (2021). Organic geochemistry of source rocks in the Baiyun Sag of the Pearl River Mouth Basin, South China Sea. Marine and Petroleum Geology, 124: 104836

[21] Leythaeuser D, Schaefer R G, Cornford C, Weiner B (1979). Generation and migration of light hydrocarbons (C₂-C₇) in sedimentary basins.Org Geochem, 1(4): 191–204

[22] Li X Y, Gong Y (2022). Differences in organic matter between coal and gangue of Shanxi Formation and Taiyuan Formation in Yanchuannan.Unconventional Oil Gas, 9(6): 27–27

[23] Li Y, Chen S J, Wang Y X, Qiu W, Su K M, He Q B, Xiao Z L (2019). The origin and source of the Devonian natural gas in the Northwestern Sichuan Basin, SW China.J Petroleum Sci Eng, 181: 106259

[24] Liu Y, Chen D, Qiu N, Fu J, Jia J (2018). Geochemistry and origin of continental natural gas in the western Sichuan Basin, China.J Nat Gas Sci Eng, 49: 123–131

[25] Lu J G, Luo Z Y, Zou H L, Li Y P, Hu Z Z, Zhou Z Y, Zhu J, Han M M, Zhao L P, Lin , Z H (2021). Geochemical characteristics, origin, and mechanism of differential accumulation of natural gas in the carboniferous kelameili gas field in Junggar Basin, China.J Petroleum Sci Engineering, 203: 108658

[26] Lu K N (2021). Study on classification and evaluation of deep source rocks and their accumulation relations in Dehui Fault Depression.Unconventional Oil Gas, (06): 14–23

[27] MilkovA V (2018). Secondary microbial gas. In: Wilkes H, ed. Hydrocarbons, Oils and Lipids: Diversity, Origin, Chemistry and Fate. Handbook of Hydrocarbon and Lipid Microbiology. Cham: Springer

[28] Peters K, Cassa M (1994). Applied source rock geochemistry. In: Magoon L, Dow W, eds. AAPG Memoir 60, the Petroleum System - from Source to Trap.AAPG, Tulsa: 93–120

[29] Prinzhofer A A, Huc A Y (1995). Genetic and post-genetic molecular and isotopic fractionations in natural gases.Chem Geol, 126(3−4): 281–290

[30] QuanY B (2018). Lacustrine source rock development mechanism and its contribution to hydrocarbon accumulation in Zhu III sub-basin, Pearl River Mouth Basin. Dissertation for Doctoral Degree. Wuhan: China University of Geosciences (in Chinese)

[31] Quan Y B, Liu J Z, Hao F, Bao X H, Xu S, Teng C Y, Wang Z F (2019). Geochemical characteristics and origins of natural gas in the Zhu III subbasin, Pearl River Mouth Basin, China.Mar Pet Geol, 101: 117–131

[32] Quan Y B, Liu J Z, Zhao D J, Hao F, Wang Z F, Tian J Q (2015). The origin and distribution of crude oil in Zhu III sub-basin, Pearl River Mouth Basin, China.Mar Pet Geol, 66(4): 732–747

[33] Su K M, Chen S J, Hou Y T, Zhang H F, Zhang X L, Zhang W X, Liu G L, Hu C, Han M M (2021). Geochemical characteristics, origin of the Chang 8 oil and natural gas in the south western Ordos Basin, China.J Petroleum Sci Eng, 200: 108406

[34] Tang L X, Zhou H, Yin L L (2022). Analysis on organic geochemistry characteristics and hydrocarbon-generating potential of coal-bearing strata in Huaibei Area.Unconventional Oil Gas, 9(6): 51–60,74

[35] Thompson K F M (1983). Classification and thermal history of petroleum based on light hydrocarbons.Geochimica et Cosmochimica Acta, 47(2): 303–316

[36] Tilley B, Mclellan S, Hiebert S, Quartero B, Veilleux B, Muehlenbachs K (2011). Gas isotope reversals in fractured gas reservoirs of the western Canadian Foothills: mature shale gases in disguise.AAPG Bull, 95(8): 1399–1422

[37] TissotB P, WelteD G (1984). Petroleum Formation and Occurrence, second ed. Berlin: Springer-Verlag, 699

[38] Wang X Z, Cao H X, Cao J (2022). Analysis of natural gas source of Lower Paleozoic in Yan’an Area, Ordos Basin.Unconventional Oil Gas, 9(6): 9–13

[39] Whiticar M (1999). Carbon and hydrogen isotope systematics of bacterial formation and oxidation of methane.Chem Geol, 161(1−3): 291–314

[40] Wood D A, Hazra B J (2017). Characterization of organic-rich shales for petroleum exploration & exploitation: a review-Part 2: geochemistry, thermal maturity, isotopes and biomarkers.J Earth Sci, 28(5): 758–778

[41] Wu C L (1984). Nan Hai (the South China Sea) movement and development of basins in the South China Sea.Mar Sci Bull, 3: 47–53

[42] Wu L Y, Gu X Z (1986). The application of pyrolysis technique in source rocks research.Acta Petrol Sin, 7(2): 13–19

[43] Xiao X M, Li N H, Gan H J, Tian H, Huang B J, Tang Y C (2009). Tracing of deeply-buried source rock: a case study of the WC9–2 petroleum pool in the Pear River Mouth Basin, South China Sea.Marine Petroleum Geo, 26: 1365–1378

[44] Xiao Z L, Chen S J, Li Y, Su K M, He Q B, Han M M (2020). Local high-salinity source rock and origin of crude oil in the Xianshuiquan Structure in the northwestern Qaidam Basin, China.J Petrol Sci Eng, 198: 108233

[45] XuX D, HuangB J (2000). A Study on the migration and accumulation of oil and gas in Qionghai ulift, Zhusan depression. Petroleum Explor Develop, 27 (4): 41–44+111–120 (in Chinese)

[46] Zumberge J, Ferworn K, Brown S (2012). Isotopic reversal (‘rollover’) in shale gases produced from the Mississippian Barnett and Fayetteville formations.Mar Petrol Geol, 31(1): 43–52

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